fix: remove artifact.file.close() that causes seek-of-closed-file error

The explicit close() on main_artifact.file broke the fallback path in
_process_metadata_batch, which calls artifact_to_metadata_artifact()
for the final batch — that function calls artifact.file.seek(0) on
the already-closed handle.

Removing the close is safe: the file handle is released when the
batch flushes and references are cleared. The temp file cleanup
(os.unlink) still happens immediately.

JIRA: PULP-1573

Author: decko

pulp_python/app/tasks/repair.py

@@ -142,10 +142,9 @@ def repair_metadata(content: QuerySet[PythonPackageContent]) -> tuple[int, set[s
                 package, new_data, batch, set_of_update_fields
             )
 
-            # Clean up temp file and close artifact file handle
+            # Clean up temp file after processing
             if temp_path and os.path.exists(temp_path):
                 os.unlink(temp_path)
-            main_artifact.file.close()
 
         # For on-demand content, we expect that:
         # 1. PythonPackageContent always has correct name and version